1. Field of the Invention
The present invention relates to novel organopolysiloxane compositions which set under hot conditions to form elastomers. These novel compositions are readily molded and extruded, making it possible, on the one hand, to quickly and completely fill mold cavities therewith, and, on the other hand, to provide extrudates which are homogeneous both at the face surfaces thereof, as well as internally. In addition to such advantages, the subject novel compositions form silicone elastomers which have a combination of remarkable properties, especially good resistance to boiling water and superior physical and electrical properties, whatever the amount of inorganic fillers contained therein.
2. Description of the Prior Art
From the very outset of the production of heat-vulcanized silicone rubbers, this art has been fraught with attempts to improve the physical characteristics thereof, especially their heat and reversion resistance.
The techniques employed therefor are widely described in the literature, patent and otherwise, including, among others, U.S. Pat. Nos. 2,803,619, 2,819,236, 3,024,126, 3,652,475, 3,660,345, 4,335,035 and 4,444,940, and British Patent No. 915,010.
U.S. Pat. No. 2,803,619 relates to compositions containing a diorganopolysiloxane resin which is devoid of vinyl radicals and a diorganopolysiloxane polymer containing a sufficient amount thereof to provide one vinyl radical per 5,000 to 20,000 silicon atoms present in the mixture of resin and polymer. These compositions set, with the assistance of an organic peroxide, to silicone elastomers which have a low residual compression set.
U.S. Pat. No. 2,819,236 relates to compositions containing a silicone resin, a diorganopolysiloxane oil having a viscosity of less than 1 million mPa.s at 25.degree. C., containing from 5 to 15 mol % of organosiloxy units, each bearing a vinyl radical, and an organic peroxide.
The elastomers produced from such compositions have low hardness and high quality mechanical properties.
U.S. Pat. No. 3,024,126 describes a process for treating a reinforcing silica with the combination of an amino compound and an organosilicon compound containing hydroxy or alkoxy radicals. Silicone elastomers containing such silica have improved physical characteristics.
British Patent No. 915,010 relates to a process for the preparation of silicone elastomers by preliminary heating of compositions containing a diorganopolysiloxane polymer, a reinforcing silica, an organosilicon compound containing hydroxy or alkoxy radicals and an amino compound selected from among ammonia or a primary, secondary or tertiary amine. The silicone elastomers have a high rupture strength and a high tear resistance, as well as improved heat resistance.
U.S. Pat. No. 3,652,475 describes compositions containing a diorganopolysiloxane resin which is devoid of vinyl radicals, a diorganopolysiloxane resin containing from 5 to 20 mol % of vinylorganosiloxy units, a diorganopolysiloxane polymer having a degree of polymerization of 10 to 1,000, containing from 5 to 90 mol % of vinylorganosiloxy units, a reinforcing silica and an organic peroxide. The silicone elastomers obtained therefrom have improved tear resistance.
U.S. Pat. No. 3,660,345 relates to compositions containing a vinyl diorganopolysiloxane resin containing 0.01 to 0.6 mol % of vinylorganosiloxy units, a vinylmethylpolysiloxane polymer added in sufficient amount to provide vinylmethylsiloxy units representing 1 to 3.5% by weight of the mixture of resin and polymer, a reinforcing silica, and an organosilicon compound which prevents structuring. The vinylmethylpolysiloxane polymer can have from 2 to 100 mol %, preferably 5 to 20 mol % of methylvinylsiloxy units. The elastomers produced from such compositions have a high resilience, as well as improved tear resistance.
U.S. Pat. No. 4,335,035 describes compositions containing a diorganopolysiloxane resin containing 0.01 to 0.3% of vinyl radicals, an organohydropolysiloxane containing 0.2 to 2.5% of vinyl radicals, a reinforcing silica and an organic peroxide. The elastomers produced from such compositions have good heat characteristics and high tear resistance.
U.S. Pat. No. 4,444,940 relates to compositions containing:
(1) a diorganopolysiloxane having a viscosity of at least 10,000 mPa.s at 25.degree. C., containing no vinyl radicals along the polymer chain; and
(2) a diorganopolysiloxane having a degree of polymerization of 2 to 400, with each end of the polymer chain blocked by a diorganovinylsiloxy unit, also devoid of vinyl radicals along the polymer chain, a reinforcing or nonreinforcing filler, and an organic peroxide [the proportion of the polymer (2) is adjusted such as to provide 0.2 to 2 diorganovinylsiloxy units per 100 diorganosiloxy units constituting said diorganopolysiloxane (1)].
The aforesaid patents, and others, emphasize improvement in the physical or heat characteristics of the product silicone elastomers. However, they neither teach nor suggest any specific means for producing elastomers which offer a combination of qualities and characteristics which can be considered desiderata in this art.
In particular, such desiderata include:
(i) easy and rapid use in molding and extrusion apparatus;
(ii) the production of extrudates which have a smooth and homogeneous surface; and
(iii) physical and electrical characteristics of a high order, whatever the selected hardness of the elastomers.